linux-kernel - Re: [PATCH v6 2/2] mm: support large folios swap-in for zRAM-like devices

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Message-ID: <ZrnHTpzp65iZqTJ5@infradead.org>
Date: Mon, 12 Aug 2024 01:26:54 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
	baolin.wang@...ux.alibaba.com, chrisl@...nel.org, david@...hat.com,
	hannes@...xchg.org, hughd@...gle.com, kaleshsingh@...gle.com,
	kasong@...cent.com, linux-kernel@...r.kernel.org, mhocko@...e.com,
	minchan@...nel.org, nphamcs@...il.com, ryan.roberts@....com,
	senozhatsky@...omium.org, shakeel.butt@...ux.dev,
	shy828301@...il.com, surenb@...gle.com, v-songbaohua@...o.com,
	willy@...radead.org, xiang@...nel.org, ying.huang@...el.com,
	yosryahmed@...gle.com, hch@...radead.org,
	Chuanhua Han <hanchuanhua@...o.com>
Subject: Re: [PATCH v6 2/2] mm: support large folios swap-in for zRAM-like
 devices

The subject feels wrong.  Nothing particular about zram, it is all about
SWP_SYNCHRONOUS_IO, so the Subject and commit log should state that.

On Sat, Aug 03, 2024 at 12:20:31AM +1200, Barry Song wrote:
> From: Chuanhua Han <hanchuanhua@...o.com>
> 
> Currently, we have mTHP features, but unfortunately, without support for large
> folio swap-ins, once these large folios are swapped out, they are lost because
> mTHP swap is a one-way process. The lack of mTHP swap-in functionality prevents

Please wrap your commit logs after 73 characters to make them readable.

> +/*
> + * check a range of PTEs are completely swap entries with
> + * contiguous swap offsets and the same SWAP_HAS_CACHE.
> + * ptep must be first one in the range
> + */

Please capitalize the first character of block comments, make them full
sentences and use up all 80 characters.

> +	for (i = 1; i < nr_pages; i++) {
> +		/*
> +		 * while allocating a large folio and doing swap_read_folio for the

And also do not go over 80 characters for them, which renders them
really hard to read.

> +static struct folio *alloc_swap_folio(struct vm_fault *vmf)
> +{
> +	struct vm_area_struct *vma = vmf->vma;
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE

Please stub out the entire function.